Prepare the brown rice according to package directions and allow it to cool to room temperature.
Slice the sushi-grade ahi tuna into uniform 1/2-inch cubes and place them in a chilled bowl.
Whisk together the tamari, toasted sesame oil, lime juice, grated ginger, and red pepper flakes to create a bright marinade.
Pour the marinade over the tuna, tossing gently to coat, then refrigerate for 10 minutes to allow the flavors to meld.
Combine the diced mango, pineapple, minced red onion, and fresh cilantro in a small bowl to create the tropical salsa.
Slice the avocado into thin, creamy wedges.
Divide the cooled brown rice into bowls and top with the marinated tuna.
Spoon the tropical salsa over the tuna and arrange the avocado wedges on the side.
Finish the dish with a sprinkle of black sesame seeds and a touch of sea salt.